This invention relates to an economical process for recovery of terephthalic acid (TPA) from various polyester waste materials.
The extensive use of polyesters and the need for disposal of polyester waste has created a great problem for many industries. In the past, polyester waste has often been used for landfills or has been incinerated because there was no economical recovery process available or the contaminants caused severe difficulties in its reapplication.
Various processes have been proposed for the recovery of TPA from various waste materials but they are very expensive, often incomplete and some release undesirable gases which pollute the atmosphere and, in general, they have not enjoyed commercial success. The most common way is to depolymerize the polyester with alkali as shown in U.S. Pat. Nos. 3,953,502 and 3,956,088.
It is the main object of this invention to provide an economical and industrially feasible process for processing all kinds of polyethylene terephthalate (PET) type waste material and for obtaining marketable TPA at low cost with substantially complete recovery.
It is intended to deal solely with solid waste material in large volumes regardless of its main origin. The solid waste scrap materials can be classified into four groups.
1. Silver-bearing films (X-ray film, exposed/non-exposed films and microfilms) PA1 2. Regular films (non-photographic, with or without another plastic coating) PA1 3. Textiles (crude polymer, yarn and fabrics) PA1 4. Bottles (clear or colored)
A general procedure is submitted herewith but is not limited as representative of a process embodying the features of this invention.